Control apparatus for jet lift aircraft



July 2, 1963 c. sNowDoN coNTRoL APPARATUS TOR JET LIFT AIRCRAFT Filed Aug. 29, 1960 United tates Patent Oliice 3,095,050l Fatented July 2, 1963 The present invention relates to laircraft of the jet lift type, that is to say, aircraft incorporating one or more jet engines so disposed as to provide a vertically `or substantially vertically downwardly directed jet eiux, the resultant upward thrust of which would support the Weight of the aircraft during take off and landing manoeuvres and has for its object to provide in such tan aircraft automatic control apparatus which will assist the pilot in maintaining a constant flight path angle in the transitional phase between ight in which the weight of the aircraft is sustained solely by aerodynamic lift derived from the wing or like surfaces, and a hovering phase lin which the sole 'support of the weight of the aircraft is derived from the downwardly `directed jet engines. lt will be understood that the reduction in aerodynamic Ililt as the aircraft decelcrates or pitches must be compensated by a change of lift engine thrust in such a manner Ias will maintain the aircraft at #a constant ilight path angle, so that when the hovering phase is reached, the lift engine thrust will exactly `oppose 'the weigh-t of the aircraft, permitting a constant rate of descent.

According to the present invention there is provided for this purpose automatic control apparatus for controlling the thrust generated by one or more vertical lift jet engines in 4an `aircraft of the type specied, said apparatus comprising in combination means for generating signals representative of the acceleration of the aircratt normal to `a desired iiight path, `and a servo system cresponsive to said signals to adjust the lift `engine thrust in such a sense as to reduce such normal acceleration.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which:

FIG. l is a block schematic diagram of automatic control apparatus according to this invention for controlling a lift yengine throttle con-trol lever in yan aircraft of the type specified.

FIG. 2 is a vector diagram of the vertical and horizontal `components of acceleration `of an aircraft embodying the apparatus shown in FIG. l.

Referring first to FIG. l, there is mounted ein `a jet lift aircraft of the type speciiied `an 'attitude `gyro 11 so arranged as to maintain a ixed attitude in relation to the earths frame of reference. The gyro 11 has iixedly thereon two accelerometers 12 :and 13, the accelerometer 12 being arranged to measure vertical acceleration of the aircraft and to generate a DC. signal the amplitude of which is a., representative of this acceleration, and the accelerometer 13 being arranged to measure the horizontal acceleration `and to generate a D.C. signal ah the Iamplitude of which is representative of the horizontal acceleration. Accelerometers 12 and 13 are of the type well-known in the art, 4as described, eg. iin Electronic ccries M lfii, vol. 2l; The Journal `of the Aero S.C.'l., vol. 7 (July 1940), pages 338-401. Signals av and ah are fed to a resolving unit 14 which may 'be Iof any known form and to which is 'also fed an input function representative of the tangle between the horizon and the desired Eight path. In this embodiment of the invention the resolving unit 14 consists of two sine-cosine potentiometers having the wipers xedly mounted on a fiight path angle `selector control shaft 15, the angular position of which is representative of the desired ilight path angle H. The resolving unit is likewise Well-known iu the art as described, eg. Components Handbook, M.I.T. Series, vol. 17, page 264. The resolving unit 14 is such as to `generate a D C. `output signal an by operating yon the input signals a,7 and av cos -i-ah sin 0 A vector diagram of the signals av, ah and an is shown in FIG. 2.

The `output signal an from the resolving unit 14 is applied to two amplitude limiters 16 and 17 to which are also fed a signal derived from a transducer mounted on -a lift engine throttle control lever 18. The output signals from the amplitude lmiters 16 `and 17 are applied .to servo ampliers 19 land 20 in which they are ampliiied and from which they yare fed rto operate a servo motor 21. 'I'he servo motor 21 drives an output shaft 2 coupled to actuate the control lever 18. As will be appreciated, the `angular displacement of the output Shaft 22 is proportional to the amplitude 'off the signal fed thereto.

A tachometer 23 is mounted on the servo motor output shaft 22 and generates a feed back signal proportional to the rate of change yof the angular position of the shaft 22. This signal is fed back to the input of each of the amplifiers 19 and 20 and `enables rate limiting of the servo motor to be made as is explained hereinafter. Also mounted on lthe motor output shaft 22 is an overspeed switch 24, duplicated for safety, which switches oif power supplies to the servo-motor 21 should this, through some faul-'t in the rate limiting arrangement, :attempt to rot-ate at 'a :speed somewhat greater than that corresponding to the rate limit.

The motor output shaft 22 is connected through a gear box clutch unit 25 the output of which is connected through a sheer pin or other safety device 27 to the lift engine throttle control lever 18. rlhe throttle control lever 18 -is connected to control the fuel output from la fuel control unit 23 supplying fuel to a lift engine 29, so that displacements of the lever 18 demand a change in lift engine thrust and hence in normal acceleration.

In operation, in response to tan acceleration fof the aircraft in a direction normal to the desired flight path, the resolving unit 14 produces Va signa-l an representative of this acceleration. This .signal lis applied to opcrate the servo motor 21 which is ananged to drive the control lever 18 in such a sense las to `adjust the fuel supply to the lift engine 29 so that the acceleration of the aircraft normal to the desired ilight path is reduced. The arrangement iis so stab-ilised that the aircraft maintains or tends to maintain the desired flight path sangle.

The `amplitude limiter 16 is such as to produce Ian output signal Ithe amplitude of which is limited to a predetermined level L so that the signal applied by it to the servo arnplilier does not exceed this level. The signal from the tachometer 23 is proportional to the rate of ychange of the langular position qb of the output shaft 22 of the servo motor 21 and is represented by the expression agb Where a is a constant and o is the `angular position of the servo motor output shaft. The signal 1.4i is applied to the servo amplifier in :a negative sense .so .that the combined applied signal is equal to the difference between the signal from the amplitude limiter 16 and the signal from the tachometer 23, and in the case where a llarge acceleration signal an is applied to the limiter 16 the combined signal is equal to L-afp This signal is amplified `and applied to drive the servo motor 21, the torque developed by the latter 'being prosnoepen L--mp Vthen the input signal to the servo motor becomes zero. The torque `applied thereto :also becomes zero and the servo motor then runs at la` steady rate given by This steady rate continues until the acceleration signal an has been reduced so tar that no `amplitude limiting occurs. When this happens qb decreases to zero.

The provision of ftwo separate parallel channels between the resolving unit 14 and the input to the servo motor 21 is a safety measure, the arrangement being such that if a Jna-ult. occurs in one lane the other lane prevents runaway.

In the case of gear box and clutch unit 25 jamming, the pilot may always mechanically uncouple his litt engine throttle control lever 18 l`from fthe servo system by `breaking the safety device Z7, leaving him in fu-ll manual control fof the fuel control unit 28 which is connected by a rigid linkage to his litt engine throttle control lever 13. Y

VIf he should wish to change the lilit engine thrust at a rate greater than the rate limit that the servo-motor 21 allows, he may override the system by slipping the clutch unit 25 without causing any damage, achieve the required .change in engine thrust, and then allow the automatic apparatus to resume control.

When hovering, the flight path selector control is switched to :a horizontal Hight path, in which case it is the output of the ventical accelerorneter alone which actuates the amplitude-limiting amplifiers 16 and '17.

From thetoregoing description of the various embodiments of this fmvention, it is evident that the objects of this invention, together with many practical |advantages fare successtully achieved. While prefenred embodiments of my invention have been described, numerous further modications may be made without departing from the scope of this invention.

Therefore, it is rto be understood thatall matters herein set forth or shown in the yaccompanying drawings are to be interpreted in :an illustrative, and not in 'a sense.

What fl claim `.as my invention and desire to secure by Letters Batent is:

1. Automatic control apparatus fork controlling the thrust lgenerated by one or more vertical litt jet engines in Ian aircraft of .the type specified, said apparatus comprising, in combination, accel'erometers for Vgenerating component signals representative of the vertical and horizontal accelerations of the aircraft, resolving means lfor deriving from said component signals'fan output signal representative `of the acceleration of Ithe .aircraft normal to any desired Hight path angle, and a servo system re- Yspolnsive to said output signal to adjust the lift engine thrust to reduce such normal acceleration.

2. Apparatus according to claim l, comprising a gyroscopic device adapted to maintain axed Iattitude in relation .to a datum plane, and wherein said accelerometers are carried by said device so as also .to maintain said lined attitude. Y

3. Apparatus according to claim k2, wherein said resolving nteans includes an electrical circuit Ito which said component signals are applied, manually adjustable means to operate on said signals :according to the angle between the datum plane and the `desired flight path.

4. Apparatus according to claim 3, wherein said manually adjustable means includes a rotatable shaft of a sine and cosine potentiometer arrangement,

5. Apparatus according to claim 1, wherein the signal representa-tive of the acceleration normal to the selected Vflight path angle is applied to operate a servo CJI motor coupled to drive a lift control lever controlling the lift engine or engines in such a way as to adjust the amount or direction of the thrust derived therefrom.

6. Apparatus according to claim l, including a servomotor, means for applying to said servo-motor signals representative of the acceleration normal to the selected flight path angle, and a lift control lever controlling the lift engine or engines to vary the amount of lift or thrust derived therefrom, said lift control lever being coupled tobe driven by said servo-motor.

7. Apparatus according to claim 6, including a tachometer connected to be driven by the servo-motor and to generate aY feedback signal portional to the rate of change of `output of the servo-motor and means to apply said feedback signal to modify the signal input to the servo-motor, said feedback signal being applied in opposition to the signal representative of the said normal acceleration.

8. Apparatus according to claim 6, including a driving connection between the output of the servo-motor and the lift control lever, said driving connection including a safety device operable by the pilot to uncouple the output of the servo-motor from said lever, thereby to permit the pilot to exercise full manual control of the lever.

9. Apparatus according to claim 6, including clutch Ymeans connecting the output of the servo-motor to the Vcomponent signals representative of the vertical and hori- Vzontal accelerations of the aircraft with respect to a horizontal datum plate lixed in space, manually adjustable resolving means to derive from said component signals an output signal representative of the acceleration of the aircraft normal to any pre-selected llight path angle, and a servo system responsive to said output signal to adjust the lift engine 'thrust to reduce such normal acceleration.

12. Automatic control apparatus for controlling the thrust generated by one Vor more vertical-lift jet engines Vin an aircraft of the type specied, said apparatus comprising, in combination, accelerometers for generating component signals representative of the vertical and horizontal accelerations of the aircraft with respect to a datum plane liXed in space, manually adjustable resolving means including an electrical circuit to which said component signals are applied and a manually adjustable control element for adjusting said circuit according to the angle between the datum plane and the desired flight path to generate an output signal representative of the accel- Y eration of the aircraft normal to the pre-selected flight ponent signals representative of the vertical and hori-` zontal accelerations of the aircraft with respect to saidV datum plane, manually adjustable resolving means including a sine and cosine potentiometer arrangement to which said component signals are applied to generate an output signal representative of the acceleration of the aircraft normal to a preselected llight path angle determined by the angular position of a rotatable shaft forming part of said sine and cosine potentiometer arrangement, and a servo system responsive to said signals to lift `the: jet engine thrust to reduce said normal acceleration.

References Cited in the le of this patent UNITED STATES PATENTS 2,691,127 Oliwa Oct. 5, 1954 6 Feucht Nov. 25, Harris Feb. 10, Metcalf July 19, Burner Mar. 28, Baliguet Apr. 11, 

1. AUTOMATIC CONTROL APPARATUS FOR CONTROLLING THE THRUST GENERATED BY ONE OR MORE VERTICAL LIFT JET ENGINES IN AN AIRCRAFT OF THE TYPE SPECIFIED, SAID APPARATUS COMPRISING, IN COMBINATION, ACCELEROMETERS FOR GENERATING COMPONENT SIGNALS REPRESENTATIVE OF THE VERTICAL AND HORIZONTAL ACCELERATIONS OF THE AIRCRAFT, RESOLVING MEANS FOR DERIVING FROM SAID COMPONENT SIGNALS AN OUTPUT SIGNAL REPRESENTATIVE OF THE ACCLERATION OF THE AIRCRAFT NORMAL TO ANY DESIRED FLIGHT PATH ANGLE, AND A SERVO SYSTEM RESPONSIVE TO SAID OUTPUT SIGNAL TO ADJUST THE LIFT ENGINE THRUST TO REDUCE SUCH NORMAL ACCELERATION. 